Light emitting diodes, know as LED or LED lamps, are used as light source in solid state lighting (SSL). LED lighting or lamps are generally classified based on the shape of reflector (MR, PAR, R, A) and socket base (GU, E, bayonet). SSLs usually comprise clusters of LEDs in a suitable housing with an electronic driver and optics including the reflector. Lamps deliver light output, generally expressed in lumens, while consuming power, expressed in watts. The efficiency or in fact the light efficiency of lamps can be expressed in lumens/watt. The inefficiency results primarily from the fact that LEDs and the electronic driver produce heat.
A problem with LED lighting is that the light produced by LEDs and the life time of LEDs is negatively influenced by the heat produced by the LED junctions and electronics in the LED lighting device. LEDs need to be cooled down as heat has a negative influence on the light output as well as the lifetime of the lamp. The life time of an LED herein is not so much to the moment in time that the LED breaks down or starts to malfunction, but the speed at which the efficiency of the LED during the functional use diminishes. The life time can be expressed for example as the functional use time after which the efficiency has reduced to below 70% of the original efficiency. This problem of heat generation and overheating is generally combated by using heat spreaders and housings of thermally conductive materials, in particular metal. Metals offer suitable thermal management solutions, but have significant drawbacks in the field of design, manufacturing and isolation for safety. For that reason, LED lamp producers started to consider replacing metal. Ceramics have been considered but use thereof is still limited, since ceramic appeared to be too brittle in several cases. Plastics, in particular thermally conductive grades, are introduced where the housing part of the LED lamps is concerned. For example in EP-1691130-A1 and WO-2006/094346-A1, LED lighting devices are described, which devices comprise a heat spreader, LEDs mounted on a PCB, a reflector, a socket and a housing. The housing is made of thermally conductive plastic material. These plastics are either too limited in their thermal conductivity, or in case plastic materials with a high thermal conductivity are used, these provide the same problems as with observed metals.
However, for general industry and consumer applications the safety requirements are steadily increasing. In particular with components made of metal and highly conductive materials introducing the risk of electrical short circuitry safety is an issue. For that reason, producers of LED lighting devices use safe electronics with insulated driver systems. Insulated driver systems however, require higher energy input for the same amount of light produced, thus not only resulting in much lower driver efficiency, but also higher heat production. The heating effect also limits the maximum power of LED lamps, which nowadays is about 11 W. Alternatively, the LED lighting device comprises an internal insulating shield, protecting the electronic components from contacting the outer parts. Such protection however also complicates or corroborates dissipation of heat produced by the electronics. Thus there is a need for a LED lighting device that is energy efficient, can be used with unsafe (i.e. non-insulated) electronic driver systems, and nevertheless complies with safety regulations and preferably can be designed as high power lamp.
The aim of the present invention is to provide a LED lighting device that is economic and efficient in light production and/or allow for a long life time of the LED light, is easy to produce and also safe. Moreover, since such lamps are becoming used more and more in the consumer area, the LED lighting devices preferably should be simple in its production and assembly, allowing for mass production.
This aim has been achieved by the LED lighting device (LLD) according to the invention wherein the LLD comprises:                a heat spreader, having a front side and a back side,        LEDs mounted on a PCB positioned on the front side of the heat spreader,        a reflector or lens, covering the LEDs,        a socket for being received by an electrical supply system,        optionally a base part,        electronic driver components mounted on the back side of the heat spreader or inside the socket or base part,        electrical leads or wiring system connecting the socket, the electronic driver components and the heat spreader,        and a housing, optionally encapsulating the electronic components and the electrical leads or wiring system, being in thermally conductive contact with the heat spreader,        wherein the housing is made of a thermally conductive, electrically conductive plastic material (TC/EC-material-A), covered with a protection layer consisting of an electrically insulating material (El-material-B) on the outside of the housing.        